A direct current (DC) to direct current (DC) converter circuit is commonly used to provide regulated voltage to various circuits and components. A DC-DC converter circuit is commonly used to provide regulated voltage to a radio frequency (RF) power amplifier circuit. A DC-DC converter circuit that provides an output voltage that is smaller than an input voltage is referred to as a buck converter. A DC-DC converter circuit that provides an output voltage that is greater than an input voltage is referred to as a boost converter. A DC-DC converter circuit that is capable of providing either an output voltage that is smaller than an input voltage or an output voltage that is greater than an input voltage is referred to as a buck-boost converter.
FIG. 1 illustrates an exemplary system 100 comprising a prior art DC-DC converter circuit 110 coupled to a prior art radio frequency (RF) power amplifier 140. The DC-DC converter 110 receives power from an external power supply or battery. The DC-DC converter 110 also receives an output voltage reference signal that gives the target output voltage to be provided by DC-DC converter 110. The output voltage reference signal is provided to DC-DC converter 110 from a control circuit (not shown) such as a baseband processor.
The output of DC-DC converter 110 is coupled to a first end of an inductor 120. A second end of inductor 120 is coupled to the radio frequency (RF) power amplifier (PA) 140. Capacitor 130 is coupled between the second end of inductor 120 and ground. The output voltage of DC-DC converter 110 provides a supply voltage for the radio frequency (RF) power amplifier (PA) 140. The output current from DC-DC converter 110 is provided to the radio frequency (RF) power amplifier (PA) 140.
FIG. 2 illustrates a block diagram showing a more detailed view of DC-DC converter 110. DC-DC converter 110 comprises a pulse width modulation (PWM) controller 210, an output switch driver 220, and a switch 230. The PWM controller 210 receives the output voltage reference signal that sets the target output voltage to be provided by DC-DC converter 110. The output of PWM controller 210 is coupled to an input of the output switch driver 220.
The output switch driver 220 controls the operation of switch 230. Switch 230 comprises a PMOS transistor and an NMOS transistor coupled in a switch configuration. Output signal lines from output switch driver 220 are coupled to the gates of the switch transistors. Output signals from output switch driver 220 control the operation of the switch transistors. The power supply voltage (VDD) for DC-DC converter 110 is coupled to the source of the PMOS transistor of switch 230. The source of the NMOS transistor of switch 230 is coupled to ground. The output of switch 230 is coupled to a first end of inductor 120.
A feedback line 240 is coupled to a second end of inductor 120. The feedback line 240 provides the output voltage signal as feedback to PWM controller 210. PWM controller 210 compares the output voltage and the output voltage reference signal. When the output voltage is less than the output voltage reference signal PWM controller 210 tries to increase the output voltage. When the output voltage is greater than the output voltage reference signal PWM controller 210 tries to decrease the output voltage. In this manner, the PWM controller 210 regulates the output voltage of DC-DC converter 110.
DC-DC converter 110 receives the output voltage reference signal and, in response, provides the target output voltage to the radio frequency (RF) power amplifier (PA) 140. In operation, the target output voltage is changed depending upon the power output requirements of radio frequency (RF) power amplifier (PA) 140. When the RF output power is high, a higher voltage is applied to the RF power amplifier 140 in order to make the power amplifier 140 work efficiently with low distortion. The output current of DC-DC converter 110 (the input current of RFPA 140) is high at this time.
On the other hand, when the RF output power is low, a lower voltage is applied to the RF power amplifier 140 in order to make the RF power amplifier 140 work efficiently. The output current of DC-DC converter 110 (the input current of RFPA 140) is low at this time.
The output current of DC-DC converter 110 (the input current of RFPA 140) and the output voltage of DC-DC converter 110 (the supply voltage of RFPA 140) typically have relationship that is illustrated in FIG. 3. When the output current is low, the output voltage is also low. When the output current is high, the output voltage is high. The coordinate points of the output current and the output voltage typically fall within the shaded area shown in FIG. 3.
For a switching DC-DC converter, it is known that using a large output switch size improves the efficiency of the DC-DC converter at heavy load but degrades the efficiency at light load. On the other hand, using a small output switch size improves the efficiency of the DC-DC converter at light load but degrades the efficiency at heavy load. This phenomenon is illustrated in FIG. 4. FIG. 4 illustrates a graph of DC-DC converter efficiency versus DC-DC converter output current for a small switch size and a large switch size. When a small switch size is used, the efficiency is better at the lower values of output current. When a large switch size is used, the efficiency is better at the higher values of output current.
If one changes the switch size according to the load (represented by the output current), the light load efficiency and the heavy load efficiency will both be improved. This result is very desirable but very difficult to achieve in practice.
In most applications, the output current dynamically changes and it is difficult to determine when the switch size should be changed (from small to large or from large to small). In addition, if the switch size is changed when the DC-DC converter is working, an undesirable voltage signal fluctuation appears on the output voltage signal.
It would be desirable to be able to change the switch size at the same time that the output current changes. However, the time that that output current changes is very difficult or impossible to detect for most applications.
In view of the deficiencies of the prior art systems, it would be advantageous to have a more efficient system and method for changing the switch size in a DC-DC converter circuit.
Before undertaking the Detailed Description of the Invention below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. The term “controller” means any device, system, or part thereof that controls at least one operation. A controller may be implemented in hardware, software, firmware, or combination thereof. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely.
Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior uses, as well as to future uses, of such defined words and phrases.